Sensors

ABSTRACT

A sensor comprising a whisker shaft and a follicle is provided. The shaft has a root end and a tip end and the shaft tapers from the root end to the tip end so that the root end is wider and the tip end is narrower. The root end is pivotably mounted in the follicle.

The present invention relates generally to sensors and particularly,although not exclusively, to whisker-based and/or whisker-like sensors,for example for challenging or hazardous environments, includingunderwater and terrestrial applications such as low or zero visibilityenvironments.

Advanced underwater operations, such as demining and maintenance of anoil rig, require intervention and surveying. A diver, or a trainedanimal like a seal, would intuitively use tactile perception to performthis task. A Remotely Operated Vehicle (ROV) equipped with anappropriate sensory and motor control infrastructure and, importantly, ahuman operator, could also perform this task.

However, divers, animals and ROVs have numerous disadvantages such asrisk to human life, fatigue, short operational range, the need ofsupport vessels and ultimately cost.

The use of AUVs is becoming a more attractive proposition when tacklingunderwater problems. However, AUVs can suffer from a paucity of sensoryinformation and this can limit close proximity work.

Some underwater tasks are still extremely difficult for an artificialautonomous agent to undertake. For example, operating in close proximityto harbour walls, seabed, and infrastructure can be particularlydifficult. This difficulty is heightened by incomplete sensor coverageof the immediate area, which is an inherent trait of conventionalsensors such as cameras and sonar.

Sonar sensors are good at long ranges of 25 m to 400 m for example, astheir field of view covers vast areas, but are effectively “blind” invery close proximity. This blind area is approximately a 0.5 m radiusaround the majority of an AUV. By “blind”, it is meant that the vehiclegains little robust and useful navigational data from these sensors, andby short range is meant from objects touching or within half a metre.Furthermore, such sensors are less reliable in cluttered and visually oracoustically occluded environments such as harbours.

As the environmental conditions become more challenging, the sensorydata becomes more unreliable. Simple, robust local awareness through theextraction of tactile information from nearby objects can be sufficientto operate in such challenging environmental conditions.

Thus, a requirement exists for improvements to be made to currentAutonomous Underwater Vehicle (AUV) technologies to allow them tooperate and interact effectively in close proximity and in visuallyoccluded environments.

The present invention seeks to provide improvements in or relating tosensors suitable for AUVs and amphibious unmanned ground vehicles(A-UGVs).

An aspect of the present invention provides an artificial whisker sensorcomprising an elongate body having a root end and a tip end, in whichthe body tapers from the root end to the tip end so that the root end iswider and the tip end is narrower, the root end is mounted in a hub,with the hub being in a suspended, free pivoting joint, and the pivotpoint of the body is at substantially the centre point of the hub.

The hub may be mounted in elastomeric material.

In some embodiments a whisker is attached to a (for examplestainless-steel) hub, which is suspended in an elastomeric material toallow it to move. In such embodiments the root end of the whisker is notattached directly to the elastomer.

A further aspect of the present invention provides an artificial whiskersensor comprising an elongate body having a root end and a tip end, inwhich the body tapers from the root end to the tip end so that the rootend is wider and the tip end is narrower, the root end is pivotablymounted in a mount in a suspended, free pivoting joint, and the pivotpoint of the body is at substantially the centre point of the mount.

The mount may be formed from an elastomeric material.

According to a further aspect of the present invention there is providedan artificial whisker sensor comprising an elongate body having a rootend and a tip end, in which the body tapers from root end to the tipend.

Taking bio-inspiration from the walrus, seal and manatee, artificialtactile whiskers are used by the present invention to address thesensory deficiency of, for example, AUVs and therefore enable reliableclose proximity work.

One feature of whisker design provided by the present invention,therefore, is a tapered whisker geometry (as opposed to, for example, aparallel, straight cylindrical, geometry).

Parallel whiskers are prone to frequency lock-in, where a narrowfrequency of vortex shedding is strongly favoured over a range of fluidvelocities. Tapered whiskers however have a broad range of shedfrequencies, and so enable significantly higher resolution of fluidvelocity (and viscosity) measurement from vortex shedding. It isexpected that for this project a broad range of frequency sensitivitiesare needed, so a cylindrical whisker will not be used. The taperedwhisker is more suitable. The taper in this experiment was from 1.5 mmat the whisker root to 0.7 mm at the tip.

The tapering may be generally constant along the length of the body.

The body may be formed from a composite material such as a glassreinforced plastics material (GRP).

The body may have a generally elongated cone shape i.e. taperinggradually and constantly from the root to the tip.

In one embodiment the body is approximately 1.5 mm at the root end andapproximately 0.7 mm at the tip end.

The present invention also provides a whisker sensor assembly comprisinga whisker sensor mounted in a housing, a magnet is attached to thewhisker and a magnetic sensor is provided in the housing to detect theposition of the magnet and hence the whisker.

The whisker may be mounted on a hub and the hub may be mounted in anelastomeric suspension.

An accelerometer may be provided at or near the base of the whisker.

The present invention also provides a whisker array comprising a clusterof a plurality of tactile whiskers. In some embodiments a clusterconsists of three tactile whiskers. A local processor may be provided.

The present invention also provides an vehicle, suitable for useunderwater, and/or in submerged conditions and/or obscured by soft,fluid or granular material, provided with one or more whisker sensorsand/or whisker assemblies and/or whisker arrays according to anypreceding claim. Some aspects and embodiments relate to a whisker arraysuitable to fit to an AUV or an A-UGV.

Some aspects and embodiments relate to whisker flow field assistedunderwater navigation.

Some aspects and embodiments relate to the use of whiskers to improvethe accuracy of underwater navigation, whilst also being covert and/oreconomical. The increase in accuracy may be achieved by using localflow-field data (fluid dynamics and interactions around an underwaterrobot) from robotic whiskers to assist IMU (inertial measurement unit)based navigation.

Existing underwater navigation systems already use acoustic based flowdata (water column) or bottom tracked velocity data to assist withinertial navigation. This data is typically gathered from a DopplerVelocity Log (DVL), which is an expensive and noisy (acoustically loud)ultrasonic sensor. Other available flow sensors, e.g. paddle andpropeller styles, are not used for navigation because they do not workwell with angled flows and turbulent flow. These are not inherent issuesfor a whisker and they can be effective flow sensors.

Artificial tactile whisker sensors formed in according with the presentinvention can, for example, provide an approach to localisation that isrobust to harsh environmental disturbances, endowing autonomous systemswith the ability to operate effectively in confined, noisy and visuallyoccludes spaces.

Marine engineering applications can benefit from such tactile sensorsdue to the lack of robust underwater close proximity sensing techniques.

An array of such tactile sensors mounted on a mobile submersible couldbe used to generate a “haptic map” of a region of the work area,containing characteristic features such as surface form, texture andcompliance. Inspiration for the design of such an array may come fromthe Walrus, which have whiskers of varying length and thickness, thatare capable of distinguishing small shapes in the silt of the seabed.

For an AUV to successfully complete an underwater task the followingcriteria may be important:

1. The AUV must maintain an accurate estimate of its location withrespect to the work area. This validates the data or interactionsundertaken, feeding into a 3D world model whiskers which will inserthigh probability information, by means of contacting and whisking thesurrounding surfaces.

2. The AUV must identify its target area/object. By palpating andprobing the target surface, additional information can be extracted suchas texture and compliance, when fused with surface form, aclassification of the area/object can be made.

3. The AUV must interact with its environment with high precision; atthe low level, whiskers will provide data to be conditioned into auseable signal by a control system, this then provides a foundation forsafe and accurate interactions.

Further aspects and embodiments may be based on one or more of thefollowing.

Using tapered compliant whiskers to measure 2D interpretation of 3Dfluid flow (currently in water, but other liquids and gases arepossible).

Machining tapered whiskers by grinding with shaped spacers or formingtapered whiskers by moulding (such as injection moulding) or by additivemanufacture.

Using clusters of 3 whiskers to measure 3D flow and flow fieldinteractions, this includes effects caused by the robot the whiskers areon and effects from the environment such as boats or river flow. Threemay be the minimum number of whiskers needed; it could be moredistributed over an underwater robot, or it could be several clusters ofthree.

Using two such clusters to measure flow round an underwater vehicle soas to assist with underwater navigation; or for other purposes, e.g.measuring flow during docking of ship's hull against dock wall.

System of 3 whiskers and a local processor (and sometimes anaccelerometer) as a packaged unit.

Using an accelerometer mounted near whisker base to identify platformvibration, which destroys whisker vortex-shedding and so interfereswith/destroys signal.

Mechanically isolating whiskers from platform (e.g. with an elasticsuspension) so as to tolerate platform vibration.

Sensing whisker motion at the whisker base (e.g. providing the whiskeras a pinned beam).

Using an elastomeric suspension, consisting of a rigid hub cast intoelastomer, so elastomer is providing both the pivot/support and therestoring force.

Sensing with a magnet in the hub and a high-frequencymagnetic-field-orientation sensor.

Using both whisker deflection and whisker vortex induced vibration tomeasure flow speed, via some algorithms we are developing.

Using hyperresolution methods to improve FFT analysis.

Using whisker deflection and whisker vibration along with a known motionto measure fluid viscosity (e.g. in silt)

Using tapered whiskers for avoiding vortex induced vibration lock-infrequency gives weaker signals but a greatly broader sensitivity.

Using whisker deflection along with a known motion to measure hardnessof a surface.

Palpating whiskers with an actuator to measure fluid viscosity; andother methods for vibrating a cylinder, including a tapered cylinder, tomeasure viscosity.

Palpating a whisker with a scanning actuator to map viscosity over avolume.

Palpating a whisker with a scanning actuator to measure surface contoursor to identify unexpected objects.

Dragging a whisker across a surface to infer textural data (e.g. paintcondition, corrosion, marine fouling).

Whiskers with a rugged type designed to work in challenging environmentssuch as maritime.

Separating the suspension/hub component from the sensor, so we caneasily swap the whisker and suspension for service without disturbingwaterproof electrical connections.

Providing whiskers on an underwater robot,

A robot for nuclear decommissioning.

A robot for hull inspection.

A robot for agri-tech and ocean monitoring/maritime robotics.

A further aspect provides a sensor comprising a whisker shaft and afollicle, the shaft having a root end and a tip end, in which the shafttapers from the root end to the tip end so that the root end is widerand the tip end is narrower, the root end is mounted in the follicle soas to provide a uniformly suspended pivot.

The pivot point of the body may be at substantially a centre point ofthe follicle.

A further aspect provides an artificial whisker sensor for takingangular measurements, comprising a beam-like body having a root end anda tip end, in which the body tapers from the root end to the tip end sothat the root end is wider and the tip end is narrower, the root end ismounted in an artificial follicle, and the beam-like body is freepivoting in the follicle.

A further aspect provides a sensor comprising a whisker shaft and afollicle, the shaft having a root end and a tip end, in which the shafttapers from the root end to the tip end so that the root end is widerand the tip end is narrower, the root end is mounted in the follicle soas to provide a uniformly suspended pivot.

The pivot point of the body may be at substantially a centre point ofthe follicle.

A further aspect provides an artificial whisker sensor for takingangular measurements, comprising a beam-like body having a root end anda tip end, in which the body tapers from the root end to the tip end sothat the root end is wider and the tip end is narrower, the root end ismounted in an artificial follicle, and the beam-like body can pivot inthe follicle.

In some embodiments the whisker root end can move smoothly over a rangeof angles.

A centre of rotation of the whisker may be in the follicle.

The follicle may include elastomeric material for providing a restoringforce for the whisker.

A further aspect provides a sensor comprising a whisker shaft and afollicle, the shaft having a root end and a tip end, in which the shafttapers from the root end to the tip end so that the root end is widerand the tip end is narrower, and the root end is pivotably mounted inthe follicle.

The whisker root end may be attached to a hub, and the hub is mounted inan elastomeric block provided in the follicle.

The whisker may tend to pivot about a point generally at the centre ofthe hub.

The pivot point of the whisker body may be at substantially a centrepoint of the follicle.

The present invention also provides a method of tactile explorationcomprising: providing one or more artificial whisker sensors, the oreach sensor comprising a tapered, elongate body; moving the whiskerthrough material of interest and in doing so causing vortex-inducedvibration; and measuring the frequency spectrum of the vibration.

The method may comprise the step of measuring and/or calculating and/orinferring whisker speed and/or material viscosity.

The method may comprise the step of measuring motion of the sensor/s atthe root end thereof.

Methods described herein may be performed using one or more whiskersensors and/or whisker assemblies and/or whisker arrays and/or a vehicleas described herein.

Different aspects and embodiments of the invention may be usedseparately or together.

Further particular and preferred aspects of the present invention areset out in the accompanying independent and dependent claims. Featuresof the dependent claims may be combined with the features of theindependent claims as appropriate, and in combinations other than thoseexplicitly set out in the claims.

The present invention is more particularly shown and described, by wayof example, in the accompanying drawings, in which:

FIG. 1 illustrates a general principle of a whisker assembly formed inaccordance with embodiments of the present invention;

FIG. 2 shows a whisker shaft is attached to a hub;

FIG. 3 shows a whisker sensor formed in accordance with an embodiment ofthe present invention;

FIG. 4 shows the variation of one measure of the spectrum (the frequencyof the strongest peak) with speed for a particular tapered whisker inwater;

FIG. 5 shows the frequency spectrum at a low speed, below thesensitivity range of the whisker under test. No significant peak isvisible;

FIG. 6 shows the frequency spectrum at a higher speed, towards thebottom of the sensitivity range, where a distinct peak is detectable;

FIG. 7 shows the frequency spectrum higher in the sensitivity range,where a very well-defined peak is visible; and

FIG. 8 illustrates one application for a whisker module formed inaccordance with the present invention.

The example embodiments are described in sufficient detail to enablethose of ordinary skill in the art to embody and implement the systemsand processes herein described. It is important to understand thatembodiments can be provided in many alternative forms and should not beconstrued as limited to the examples set forth herein.

Accordingly, while embodiments can be modified in various ways and takeon various alternative forms, specific embodiments thereof are shown inthe drawings and described in detail below as examples. There is nointent to limit to the particular forms disclosed. On the contrary, allmodifications, equivalents, and alternatives falling within the scope ofthe appended claims should be included. Elements of the exampleembodiments are consistently denoted by the same reference numeralsthroughout the drawings and detailed description where appropriate.

Unless otherwise defined, all terms (including technical and scientificterms) used herein are to be interpreted as is customary in the art. Itwill be further understood that terms in common usage should also beinterpreted as is customary in the relevant art and not in an idealisedor overly formal sense unless expressly so defined herein.

In the description, all orientational terms, such as upper, lower,radially and axially, are used in relation to the drawings and shouldnot be interpreted as limiting on the invention.

FIG. 1 illustrates a general principle of a whisker assembly formed inaccordance with embodiments of the present invention.

The assembly has a machined Delrin (or other marine grade material)housing containing epoxy-potted electronics, an elastomeric whiskersuspension, and a glass-reinforced plastic (GRP) whisker. It usesmarine-grade materials and is designed to be submerged. Submerged depthis limited by the depth ratings of the cable and connectors used, andnot the design of the whisker itself. The whisker design has no areas ofpressure differences and is solid state in other parts, so is predictedto be functional at depths in the magnitude of kilometres deep.

The sensing principle involves a permanent magnet attached to thewhisker base and a magnetic sensor (for example Melexis MLX90333 orMLX90363) detects the position of the magnet, and hence the position ofthe whisker.

In some embodiments the whisker assembly is designed so the whiskerattaches to a hub with a flange, which sits inside a cylindrical recesswith openings at top and bottom for the whisker shaft and the magnet. Itallows testing of two kinds of suspension—either a pair of O-rings, or acast-in-place elastomer. O-rings have the practical advantage that theyare commercially available in a range of materials and Shore A hardness.Cast-in-place allows access to a different selection of materials, andalso allows a slightly different mechanical behaviour, since it fillsthe cavity completely.

The O-ring design offers high quality and uniform material, but has beenshown in experiments for this project to be unsuitable for sensingVortex Induced Vibrations (VIV). To sense VIV the material must becompliant enough to allow movement by the small forces generated by thespecific vortices shed by the specific whisker. The compliant materialmust also be elastic enough to restore to the centre position and notaccumulate significant deformation. The compliant material used in someembodiments is polyurethane with a stiffness of approximately Shore A20.

The artificial whisker therefore may consist of a flexible shaft mountedinto a polyurethane filled casing referred to as the whisker follicle.In some embodiments the end of the mounted whisker shaft is effectivelya ball joint which is designed to pivot above a Hall Effect sensor IC.

A small neodymium magnet is bonded to the mounted base of the whiskersuch that it conveys the 2D angular pivot position of the whisker shaft.This assembly is mounted into a follicle holder which houses thetri-axis Hall effect sensor IC (e.g. Melexis MLX90363, MLX90393 orMLX90333) which is aligned such that the magnet attached to the whiskershaft is suspended directly above the Magneto-Concentrator on the IC.This programmable sensor can be configured to generate digital signalsor analogue output voltages, proportional to the degree of displacementof the magnetic field in the orthogonal axes from a calibrated zeroposition. The third axis, which is in-line with the whisker shaft, hasbeen physically constrained. Therefore, any deflections of the whiskershaft can be measured as a proportional displacement vector at the baseand captured using a computer or microcontroller or a standard Analogueto Digital Converter (ADC) at a maximum sample rate of, for example, upto 2 KHz, for example up to 1.5 KHz or up to 1 kHz.

The whisker assembly may sense motion of the whisker shaft at the baseof the shaft, where the magnet is located. Deflection of the shaftrotates the magnet about a pivot point. Utilisation of a magnet andTri-axis Hall Effect sensor offers a 2 kHz sampling rate and a robustnon-contact solution. In some embodiments the whisker can sense both ACand DC deflections, so therefore can sense a static deflection (i.e.force loading), and oscillating deflection (i.e. vibration).

In some embodiments the sampling electronics consists of a custom-builtPrinted Circuit Board (PCB) and a dsPIC30f4011 micro-controllerprogrammed to sample the analogue voltages across all 6 channels of a 3whisker array at 500 Hz. The micro-controller relays this informationvia a Universal Asynchronous Receiver/Transmitter (UART) serial port insingular whisker mode, or via a combination of UART and SerialPeripheral Interface (SPI) to a FTDI FT232R USB bridge for highbandwidth communications. Both communications use a standard desktopcomputer as an end point for logging, live processing and offlineanalysis.

As shown in FIG. 2 a whisker shaft is attached to a hub. The hub issuspended in a rubbery polyurethane block, which means it tends to pivotabout a point at the centre of the hub (which may or may not be at thecentre of a follicle).

FIG. 3 shows a whisker sensor formed in accordance with an embodiment ofthe present invention.

The whisker is tapered from its (narrower) tip end to its (wider) rootend. The root end is mounted in a follicle case. The whisker root end isattached to a hub and the hub is suspended in an elastomeric block toprovide a pivoting joint (i.e. not a cantilevered joint). The hub canmove in X, Y and Z directions and the centre of rotation of the whiskeris at the centre of the hub (and not, for example, at the base of thewhisker). The whisker follicle arrangement includes a magnet which islocated above a sensor for detecting movement.

The whisker is attached to a stainless-steel hub, which is suspended inan elastomeric material to allow it to move. In this embodiment the rootend of the whisker is not attached directly to the elastomer.

The whisker can move smoothly over a range of angles, the centre ofrotation is in the follicle, but there's a restoring force from theelastomer. The elastomer constrains the pivoting motion.

FIG. 4 shows the variation of one measure of the spectrum (the frequencyof the strongest peak) with speed for a particular tapered whisker inwater.

FIG. 4: When a whisker is moved through a fluid, vortex-inducedvibration is caused. With a whisker of any shape, the frequency spectrumof this vibration varies with speed and viscosity, and so the spectrumcan be used to infer speed. With a tapered whisker, this variation is aparticularly useful measure.

FIGS. 5-7 show spectra at three different speeds, illustrating how thespectrum changes with speed.

FIG. 5 shows the frequency spectrum at a low speed, below thesensitivity range of the whisker under test. No significant peak isvisible.

FIG. 6 shows the frequency spectrum at a higher speed, towards thebottom of the sensitivity range, where a distinct peak is detectable.

FIG. 7 shows the frequency spectrum higher in the sensitivity range,where a very well-defined peak is visible.

FIG. 8 illustrates one application for a whisker module formed inaccordance with the present invention. In this embodiment a whisker isprovided on a module which in turn is mounted on a robot arm. Thewhisker shaft can, for example, be rotated to and fro, to cause it topass through the sediment. When the shaft contacts an object this can berecorded and a picture of the environment can be built up.

This arrangement can be used as part of a tactile sensing system and tomeasure viscosity and flow speed across the whisker.

If the whisker is swept at a known speed it is possible to calculateviscosity of the medium through which the whisker is being moved. If thewhisker is being moved through a medium of known viscosity it ispossible to calculate the velocity.

Further examples of aspects and embodiments are listed in the followingnumbered paragraphs.

1. An artificial whisker sensor comprising an elongate body having aroot end and a tip end, in which the body tapers from the root end tothe tip end so that the root end is wider and the tip end is narrower,the root end is mounted in a hub, with the hub being in a suspended,pivoting joint, and the pivot point of the body is at substantially thecentre point of the hub.

2. A sensor as claimed in paragraph 1, in which the hub is mounted inelastomeric material.

3. A sensor as claimed in paragraph 1 or paragraph 2, in which thetapering is generally constant along the length of the body.

4. A sensor as claimed in any preceding paragraph, in which the body isformed from a composite material.

5. A sensor as claimed in paragraph 4, in which the body is formed fromGRP.

6. A sensor as claimed in any preceding paragraph, in which the body hasa generally elongated cone shape.

7. A sensor as claimed in any preceding paragraph, in which the body isapproximately 1.5 mm at the root end and approximately 0.7 mm at the tipend.

8. A whisker sensor assembly comprising a whisker sensor mounted in ahousing, a magnet is attached to the whisker and a magnetic sensor isprovided in the housing to detect the position of the magnet and hencethe whisker.

9. An assembly as claimed in paragraph 8, in which the whisker ismounted on a hub and the hub is mounted in an elastomeric suspension.

10. An assembly as claimed in paragraph 8 or paragraph 9, in which anaccelerometer is provided at or near the base of the whisker.

11. A whisker array comprising a plurality of whiskers and a localprocessor.

12. An array as claimed in paragraph 11, in which the array consists ofthree whiskers.

13. A whisker array comprising a cluster of three whiskers and a localprocessor.

14. An artificial whisker sensor comprising an elongate body having aroot end and a tip end, in which the body tapers from root end to thetip end.

15. A sensor comprising a whisker shaft and a follicle, the shaft havinga root end and a tip end, in which the shaft tapers from the root end tothe tip end so that the root end is wider and the tip end is narrower,the root end is mounted in the follicle so as to provide a uniformlysuspended pivot.

16. A sensor comprising a whisker shaft and a follicle, the shaft havinga root end and a tip end, in which the shaft tapers from the root end tothe tip end so that the root end is wider and the tip end is narrower,and the root end is pivotably mounted in the follicle.

17. A sensor as claimed in paragraph 15 or paragraph 16, in which theroot end is attached to a hub, and the hub is mounted in an elastomericblock provided in the follicle.

18. A sensor as claimed in paragraph 17, in which the whisker tends topivot about a point generally at the centre of the hub.

19. A sensor as claimed in paragraph 17 or paragraph 18, in which thepivot point of the body is at substantially a centre point of thefollicle.

20. An artificial whisker sensor for taking angular measurements,comprising a beam-like body having a root end and a tip end, in whichthe body tapers from the root end to the tip end so that the root end iswider and the tip end is narrower, the root end is mounted in anartificial follicle, and the beam-like body can pivot in the follicle.

21. A sensor as claimed in paragraph 20, in which the whisker root endcan move smoothly over a range of angles.

22. A sensor as claimed in paragraph 20 or claim 21, in which a centreof rotation of the whisker is in the follicle.

23. A sensor as claimed in any of paragraphs 20 to 23, in which thefollicle includes elastomeric material for providing a restoring forcefor the whisker.

24. An underwater vehicle provided with one or more whisker sensorsand/or whisker assemblies and/or whisker arrays according to anypreceding paragraph.

25. A remotely operated vehicle provided with one or more whiskersensors and/or whisker assemblies and/or whisker arrays according to anyof paragraphs 1 to 23.

26. A method of tactile exploration comprising: providing one or moreartificial whisker sensors, the or each sensor comprising a tapered,elongate body; moving the whisker through material of interest and indoing so causing vortex-induced vibration; and measuring the frequencyspectrum of the vibration.

27. A method as claimed in paragraph 26, comprising the step ofmeasuring and/or calculating and/or inferring whisker speed and/ormaterial viscosity.

28. A method as claimed in paragraph 26 or paragraph 27, comprising thestep of measuring motion of the sensor/s at the root end thereof.

29. A method as claimed in any of paragraphs 25 to 28, performed usingone or more whisker sensors and/or whisker assemblies and/or whiskerarrays and/or a vehicle according to any of paragraphs 1 to 25.

Combinations of different aspects and embodiments may be made.

Although illustrative embodiments of the invention have been disclosedin detail herein, with reference to the accompanying drawings, it isunderstood that the invention is not limited to the precise embodimentsshown and that various changes and modifications can be effected thereinby one skilled in the art without departing from the scope of theinvention as defined by the appended claims and their equivalents.

1. A sensor comprising a whisker shaft and a follicle, the shaft havinga root end and a tip end, in which the shaft tapers from the root end tothe tip end so that the root end is wider and the tip end is narrower,and the root end is pivotably mounted in the follicle.
 2. A sensor asclaimed in claim 1, in which the root end is attached to a hub.
 3. Asensor as claimed in claim 2, in which the hub is mounted in anelastomeric block located or provided in or by the follicle.
 4. A sensoras claimed in claim 2, in which the whisker tends to pivot about a pointgenerally at the centre of the hub.
 5. A sensor as claimed in claim 1,in which the pivot point of the body is at substantially a centre pointof the follicle.
 6. A sensor as claimed in claim 1, in which thetapering is generally constant along the length of the shaft.
 7. Asensor as claimed in claim 1, in which the whisker shaft is formed froma composite material.
 8. A sensor as claimed in claim 7, in which thewhisker shaft is formed from GRP.
 9. A sensor as claimed in claim 1, inwhich the whisker shaft has a generally elongated cone shape.
 10. Asensor as claimed in claim 1, in which the shaft is approximately 1.5 mmat the root end and approximately 0.7 mm at the tip end.
 11. A sensor asclaimed in claim 1, in which a magnet is attached to the whisker and amagnetic sensor is provided in the follicle to detect the position ofthe magnet and hence the whisker.
 12. A sensor as claimed in claim 1, inwhich an accelerometer is provided at or near the root end of thewhisker.
 13. A whisker array comprising a plurality of whiskers asclaimed in claim
 1. 14. An array as claimed in claim 13, furthercomprising a local processor.
 15. An array as claimed in claim 13, inwhich the array consists of three whiskers.
 16. A vehicle provided withone or more sensors according to claim
 1. 17. A method of tactileexploration comprising: providing one or more artificial whisker sensorsfor taking angular measurements, the or each sensor comprising atapered, elongate body; moving the whisker through material of interestand in doing so causing vortex-induced vibration; and measuring thefrequency spectrum of the vibration.
 18. A method as claimed in claim17, comprising the step of measuring and/or calculating and/or inferringwhisker speed and/or material viscosity.
 19. A method as claimed inclaim 17, comprising the step of measuring motion of the sensor/s at theroot end thereof.
 20. A method as claimed in claim 17, performed usingone or more sensors according to claim 1.